In an SPM or AFM, prior to scanning the sample surface, usually two engagement steps take place. In a first coarse engagement step, a cantilever-type probe is moved from a few millimeters (or even centimeters) above the sample surface to a position less than 1 millimeter (for instance a few 100 μm) above. After this step, a fine engagement is started, where the cantilever is moved continuously or in steps of a few micrometers until it reaches its final starting position for the measurement.
During such engagement steps as well as during an actual sample analysis where a probe scans the sample, care should be taken that neither the probe nor the sample is damaged by a collision between probe and sample. This problem is particularly pronounced when analyzing samples with complex shape.
U.S. Pat. No. 9,448,393 discloses a scanning probe microscope (SPM) used to investigate or measure large samples whose size is a multiple of the typical operational scanning area of an SPM. To avoid frequent readjustments or other time-consuming human interaction and errors when focusing the SPM, a multi-step, automated method for the SPM-scanning of large samples is disclosed, comprising a coarse, i.e. low resolution, non-SPM scanning or mapping step adapted to scan a large sample and providing an integral map of the sample, followed by a preferably mathematical evaluation step identifying areas of interest of the sample, which areas are then subjected to a focused fine raster scanning step by the SPM with high resolution.
U.S. Pat. No. 7,430,898 discloses a system that includes an optical subsystem and an atomic force microscope probe. The optical subsystem is configured to generate positional information about a location on a surface of the specimen. The system is configured to position the probe proximate the location based on the positional information. A method includes generating positional information about a location on a surface of a specimen with an optical subsystem. The method also includes positioning an atomic force microscopy probe proximate the location based on the positional information. Another system includes an optical subsystem configured to measure overlay of a wafer using scatterometry. The system also includes an atomic force microscope configured to measure a characteristic of a feature on the wafer. An additional method includes measuring overlay of a wafer using scatterometry. The method also includes measuring a characteristic of a feature on the wafer using atomic force microscopy.
However, in particular when a sample has a complex shape, it may still happen that the probe with its highly sensitive tip may unintentionally collide with the sample which may destroy the probe, the sample and/or the analysis. Conventional approaches intending to partially overcome such shortcomings lack precision and are cumbersome.